Improvement of Electromagnetic Field Distributions Using High Dielectric Constant (HDC) Materials for CTL-Spine MRI: Numerical Simulations and Experiments

Abstract

This study investigates the use of pads with high dielectric constant (HDC) materials to alter electromagnetic field distributions in patients during magnetic resonance imaging (MRI). The study was performed with numerical simulations and phantom measurements. An initial proof-of-concept and validation was performed using a phantom at 64 MHz, showing increases of up to 10% in electromagnetic field when using distilled water as the high dielectric material. Additionally, numerical simulations with computational models of human anatomy were performed at 128 MHz. Results of these simulations using barium titanate (BaTiO3) beads showed a 61% increase of ∣bold-italicB1+∣ with a quadrature driven RF coil and a 64% increase with a dual-transmit array. The presence of the HDC material also allowed for a decrease of SAR up to twofold (e.g., peak 10 g-averaged SAR from 54 to 22 W/kg with a quadrature driven RF coil and from 27 to 22 W/kg with a dual-transmit array using CaTiO3 powder at 128 MHz). The results of this study show that the use of HDC pads at 128 MHz for MRI spine applications could result in improved magnetic fields within the region of interest, while decreasing SAR outside the region.

Reducing RF-Induced Heating Near Implanted Leads Through High-Dielectric Capacitive Bleeding of Current (CBLOC)

“…Their application in the context of MRI however, is relatively new. Pioneering work has been done by the Webb group advancing the use of HDC pads to increase the signal to noise ratio during high-field MRI [42,[66][67][68]. Recently, the use of external HDC pads in regions not directly adjacent to the implant cite has been shown to reduce the SAR at the tip of medical implants [69].…”

Reducing RF-induced Heating near Implanted Leads through High-Dielectric Capacitive Bleeding of Current (CBLOC)

“…Their application in the context of MRI however, is relatively new. Pioneering work has been done by the Webb group advancing the use of HDC pads to increase the signal to noise ratio during high-field MRI [42,[65][66][67]. Recently, the use of external HDC pads in regions not directly adjacent to the implant cite has been shown to reduce the SAR at the tip of medical implants [68].…”

Novel Method to Improve the Uniformity of 7T Body MR Images

“…To acquire magnetic resonance (MR) images of high resolution and increased signal-to-noise ratio (SNR), a higher static magnetic field (|B 0 |) is needed [1][2][3][4][5][6]. is is because the intrinsic SNR (ISNR) in magnetic resonance imaging (MRI) is proportional to the square of |B 0 |(ISNR ∝ |B 0 | 2 ) [1,2].…”

“…is is because the intrinsic SNR (ISNR) in magnetic resonance imaging (MRI) is proportional to the square of |B 0 |(ISNR ∝ |B 0 | 2 ) [1,2]. However, as |B 0 | is increased, the absorbed power increases significantly [5,7], and magnetic field inhomogeneity caused by a wavelength effect results in decreased image intensity uniformity [6][7][8]. ese effects are significant in the imaging of human tissue using 7T MRI systems [6], the highest field approved for MRI by the FDA.…”

“…Many different methods have been studied to solve the issues of image uniformity and absorbed power of high-field MRIs. Some of the examples are multichannel excitation using a shielded birdcage coil [9,10], transmit array with radiofrequency (RF) shimming [11][12][13][14][15], composite pulse [16,17], spoke pulse [18][19][20], different transmit RF coil designs [21][22][23][24], high dielectric constant (HDC) materials [5,7,[25][26][27][28], and simultaneous transmit excitation of phased array and volume coil [8]. Specifically, Taracila [9] showed image uniformity was improved by applying a series of multiple current distributions on the entire birdcage coil using different modes of the birdcage coil and then combining individually acquired images at 300-400 MHz.…”